After some thought, below are listed some of the things Psiloi can do in DBA 3.0:
* Psiloi are the only troops that can interpenetrate. This means they can be used as a screen in front of the main battle line and fall back through it.
* Psiloi are the only infantry that can make a subsequent move during a bound.
* Psiloi are fast foot, moving 3 base widths.
* Psiloi are not effected by bad going terrain.
* Psiloi cannot be corner overlapped in close combat - in straight up melee they always fight at +2. However, they are still effected by flank/rear edge overlap by enemy elements.
* Psiloi cannot be destroyed in frontal combat by heavy infantry - they flee instead.
* Pikes & Warband do not get a rear rank bonus against Psiloi, therefore Psiloi usually fight them +2 vs +3.
* Psiloi can "quick kill" elephants in melee - they destroy them if they beat them by just 1 pip. However, the psiloi fight elephants at +2 vs +5, so this isn't easy, unless the psiloi also has overlapping friends.
* Tactically, I believe they are useful on the flanks supporting cavalry, where they can be used to interpenetrate and flank the enemy, and able to run for cover in bad going using regular or subsequent moves. They are also useful for harassing the enemy out of bad going.
* Enemy pike, blade, & spear do not pursue Psiloi when beaten in close combat.